1. Field of the Invention
The present invention relates to an electron emitting device applicable to a display, an exposure device or the like and a method of manufacturing the electron emitting device, and particularly relates to a cold cathode type electron emitting device having a planar structure and the method of manufacturing the device.
2. Description of the Related Art
In recent years, a cold cathode type electron emitting device having a planar structure has been proposed. This kind of device referred to as a surface conduction type device or planar type MIM device has a pair of electrodes formed at a certain interval on a flat insulating substrate, a pair of conductive films formed between these electrodes and electron emitting films formed on these conductive films. Since such an electron emitting device has a simple structure, it is suitable for forming an electron source array by arraying a large number of the devices on the same substrate.
As an application of such an electron source array, a thin type planar display now attracts attentions. This display is the one in which phosphors are made excited by electrons to emit lights similarly to a CRT. Since luminescence on the basis of such a principle has a high performance in energy efficiency, by employing the above-described electron source array, it is possible to realize a self light-emitting and thin type planar display whose power consumption is low and which displays an image with a high luminance and a high contrast.
One example of a planar type MIM device has been reported, for example, in Int. J. Electronics, 73 (1992) 1009 and Int. J. Electronics, 70 (1991) 491 by Bischoff et al., the entire contents of which are incorporated herein by reference. FIG. 1 is a perspective view schematically showing a device that Bischoff et al. has reported. The reference numeral 100 denotes an insulating substrate, the reference numerals 101a and 101b denotes metal electrodes, the reference numeral 102 denotes a metal film provided with a micro-slit, and the reference numeral 103 denotes a deposition film provided at the position of the micro-slit. Moreover, the reference numeral 105 denotes the width of a micro-slit provided to the metal film 102, and its width 105 ranges from on the order of 0.1 μm to 10 μm.
Such a structure is formed according to the following procedure. First, a pair of planar metal electrodes 101a and 101b are formed on the insulating substrate 100. Next, the metal film 102 being sufficiently thin as compared with the electrodes 101a and 101b and having a sufficient thickness for electrically conductive is formed. Next, Joule heat is generated in the metal film 102 by the passage of electric current between the electrodes 101a and 101b. Consequently, the metal film 102 is partially fused and destroyed to be discontinuous. Specifically, a micro-slit is formed in the metal film 102. It should be noted that resistance between the electrodes 101a and 101b is high immediately after the electrically conductive film is made discontinuous. Bischoff et al. refers such a procedure of making the electrically conductive film discontinuous by the current flow through the film as “B-forming (basic forming)”.
The procedure referred to as “A-forming (adsorption-assisted forming)” is further performed to the structure thus formed. In the A-forming, a voltage of 20V or less is applied between the electrodes 101a and 101b in a vacuum containing hydrocarbons. Consequently, hydrocarbon molecules adsorb on the portion of the substrate 10 exposed within the micro-slit and forms the deposition film 103. As a result, the resistance between the electrodes 101a and 101b is lowered in a few minutes after the voltage application, and the electric current which flows between the electrodes 101a and 101b increases.
Bischoff et al. have reported in the previous literature that in addition to an electron emitting, a light emitting is observed by the passage of electric current through the device after the A-forming is performed. Bischoff et al. have estimated that a material of the deposition film 103 must be the one which can contain thermoelectron to 4,000 kelvin and in which the material itself can be heated to the temperature exceeding 1,000 kelvin. Based on the estimation, Bischoff et al. have discussed that the deposition film 103 is a carbon film graphitized.
Another example of a planar type MIM device has been reported, for example, by Pagnia et al. in Phys. Stat. Sol. (a) 108 (1988) 11, the entire contents of which are incorporated herein by reference. In a device of Pagnia et al., a ratio of an emission current to an electric current (device current) inputted to the device, i.e., the emission efficiency is extremely small and on the order of 10−6, a voltage-current curve thereof indicates a VCNR characteristic (Voltage-Controlled Negative Differential Resistance characteristic) as shown in FIG. 2.
A surface conductive type device has a structure similar to a planar type MIM device and one example thereof has been reported, for example, in Japanese Unexamined Patent Publication No. 11-297192. In the manufacturing processes of the surface conductive type device, as similarly to the planar type MIM device previously described, an electrically discontinuous section is formed in a thin film by the step which is referred to as a forming, and a material containing carbon is deposited on the thin film by the step which is referred to as an activation. Differently from the afore-mentioned planar type MIM device, a surface conductive type device, for example, described in Japanese Unexamined Patent Publication No. 11-297192 does not have the VCNR characteristic as shown in FIG. 3 but does exhibit a monotonously increasing type voltage-current curve. Moreover, an emission efficiency of the surface conductive type device is on the order of 10−3 and is higher that of the planar type MIM device. With regard to this feature, the surface conductive type device and the planar type MIM device are characteristically different from each other.
As described above concerning with a planar type MIM device, in a planar type electron emitting device, a portion nearby the electron emitting section becomes in extremely a high temperature. Therefore, in a planar type electron emitting device, a thin film functions as an electron emitting section is easily degenerated, therefore, the characteristic of the device may be deteriorated with time. Therefore, in a planar type electron emitting device, it is desired that the long term stability is enhanced.
Moreover, in the case where the planar type electron emitting devices are applied to a display, a voltage drop more or less occurs, and the voltage drop becomes more prominent when a large number of pixels on the identical wiring are lighted at the same time by line-sequential drive. In the case where an emission efficiency of each device is low, the voltage drop becomes significantly large, and as a result, unevenness of luminance occurs. Therefore, it is desired for a planar type electron emission device to be capable of realizing a higher electron emission efficiency.
Thus, it is desired for a conventional planar type electron emitting device to enhance the long term stability and electron emission efficiency, that is, it is desired for it to enhance the device characteristic.